Battery/electric question

[neil omalley]

So, yesterday I was concerned with changing out my chassis batteries. Today I've got another concern.When I left my coach last night after charging the batteries I turned OFF the chassis batteries . I went to the coach today and tried to start my genset and couldn't until I pushed the battery assist button. It started immediately, which suggest my particular coach's generator starts from the chassis battery bank? However, the chassis batteries were still shut off. At that point I turned my engine key and it stated right away. (with the battery switch still off) . Anyone with an idea what's going on? How come the engine started with the batteries off. How come the generator started with the batteries off ? Should not the generator have started without pushing the assist button. Do I sound confused ? I am? Any help??

[Gerald Farris]

Neil,
I think that most of your confusion here rest in the fact that you think that turning the switch off that is marked "chassis batteries" actually disconnects everything from the chassis batteries. There are several functions that do not run through that switch like the starter motor and ECM, and therefore the chassis batteries can still be discharged by things like the ECM (engine control module) unless you remove a battery cable or install a disconnect at the battery.

Gerald

[Edward Buker]

Neil,

You may want to post what year and model of coach that you have. It is clear from your post that the chassis battery normally supplies the generator the way you are wired now. I think that the battery leads between the house and chassis bank at some point could have been switched or you have a large solenoid enabled that is supplying power to the chassis leads with the chassis batteries switched off. I would take a meter and measure the copper busses in the electrical bay to ground with the house switch on and off and the chassis switch on and off. That should tell you what switch controls the engine starter circuit. If it was the house switch I would look to possibly exchange the plus leads between the two banks. You should also verify that the house switch is controlling the house lights, if not then the exchange of the two battery bank hot leads is in order.

One caution, depending on how you are wired it is possible to ruin an alternator by removing the battery bank as a load. Some generators have a small alternator built in for instance. If you start the generator using the battery assist and the chassis battery switch is off and then you release the assist button once started, that can leave the alternator disconnected from a battery bank which can damage it. It is best if you are going to run an engine with an alternator on it to have the battery switches both on given we do not always know how things are wired. It is OK to couple banks with the assist and release it to disconnect the banks from each other given the battery switch is on so the alternator is still coupled to at least one battery bank. Sometimes alternator outputs are wired in beyond the switches to the battery bank to avoid this issue. It is just that we never know how we are wired for sure...

Later Ed

[neil omalley]

Hi Gerald. The starter motor is still energized with he battery switch off ? What then does the switch turn off?
Ed: I'm going to test the busses as soon as I figure out how to use the meter
Thanks guys !

[Gerald Farris]

Neil,
The wiring that runs through the battery cut off switches varies between coaches, and since you did not list what model coach you have, I would be just guessing if I tried to answer your question. The best way to answer your question is to just take a meter and check the circuits that are powered with the switch on and off. It is a possibility that you have a bad or miss-wired switch, but that can only be determined by checking the circuits.

Gerald  

[Steve Huber Co-Admin]

Neil,
From what you area describing, it sounds like your coach is wired as folllows;
 
-12v from the chassis batteries is wired directly to the engine starter and the ECU.
- A second line goes to the battery isolator and to the boost start solenoid and then to the chassis battery cut-off switch.
-The generator is tied to the input line of the chassis battery cutoff switch rather than to the output of it.

Thus, the engine, but not the generator, will start when the chassis battery switch is off.

-The house batteries are connected to the isolator and then the boost start solenoid and then to the coach battery cutoff switch.

So, when you press the battery boost switch, you are supplying 12v from the coach batteries to the generator through the boost solenoid. Under normal conditions (chassis batteries connected) the generator gets its 12v from the chassis batteries.

(If wired this way, you should be able to start the generator via the boost switch, even if the house battery switch is off).

Steve

[Steve Huber Co-Admin]

Neil,
Correction;

-12v from the chassis batteries is wired directly to the engine starter and the ECU.
- A second line goes to the battery isolator and to the boost start solenoid
-The chassis battery cutoff switch is located between the chassis batteries and the boost start solenoid.
-The generator is tied to the chassis battery at the boost start solenoid..

Thus, the engine, but not the generator, will start when the chassis battery switch is off.

-The house batteries are connected to the isolator and then the boost start solenoid and then to the coach battery cutoff switch.

So, when you press the battery boost switch, you are supplying 12v from the coach batteries to the generator at the boost solenoid. Under normal conditions (chassis batteries connected) the generator gets its 12v from the chassis batteries.

Steve

[neil omalley]

Thanks guys. This is why I always had an engineer with me when I flew.   Gerald, I have an '05 Thunder. I'll probably have someone who knows (like you guys) point to things and tell me "this does that,that does this" . Or maybe just rewire so I know what to expect.

[Edward Buker]

The main starter lead from the chassis batteries will go directly to the starter but the busses up front in the electrical bay and therefor the dash ignition switch etc should not work without the chassis battery switch on. That is my recollection on mine anyway.

If it was wired any other way I would not know why you even had a chassis battery switch....

Later Ed

[neil omalley]

Yeah, that's kinda what I was thinking,Ed. I always thought a cutoff switch - cutoff stuff. (Not necessarily,eh)

[Gerald Farris]

Neil,
Since your coach is an 05, it does not have a battery isolator. The 05 coaches used a "Bird" system instead. With the "Bird" system, if either battery bank is being charged, all of the batteries are tied together with the "Big Boy" solenoid.

Gerald    

[Steve Huber Co-Admin]

OK, now symptoms make more sense. I thought it was an earlier year coach.
Steve

[neil omalley]

So am I understanding that as long as either set of batteries are being charged by the onboard charger and/or the alernator that the switches really are not functional ? and that ALL of the batteries are being charged equally? Or does the "bird" system act as an isolator whereby the chassis set is charged via the alernator and when full allow a "trickle" charge to the house?and the house are charged via the charger part of the xantrex and when THEY are full allow a "trickle charge" to the chassis? (I hate electricity )

[Joel Ashley]

You're getting the idea, Neil, but things are charged as needed... not necessarily a trickle.  The BIRD electronically controls things regarding battery charging, but does it via the Big Boy solenoid that is the "isolator".  

But I'm "shocked"   to hear you hate electricity like me!

Joel

[Gerald Farris]

Neil,
The "Bird" system does not trickle charge either sets of batteries. The engine alternator is connected to the chassis batteries and charges them to a preset voltage. As soon as the preset voltage is reached, both battery banks are tied together by the "Big Boy" and charged equally. The same thing happens when the inverter is charging the house batteries. The D in "Bird" stands for the delay as the "Bird" module is waiting for the proper voltage to be reached before combining the battery banks to charge them both equally.

Battery isolation is achieved with a "Bird" system because the only time that the batteries are tied together is when they are being charged. At all other times the battery banks are completely separated, and therefore one battery bank can not discharge the other.  

Gerald